Slow release production of chlorine dioxide from acidified sodium chlorite

ABSTRACT

A sodium chlorite (NaClO 2 ) solution is admixed with flowing water to form a flowing water and sodium chlorite (NaClO 2 ) solution. A flowing water and acid solution is admixed into the flowing water and sodium chlorite (NaClO 2 ) solution. The combined solutions are directed into and through a mixing chamber to form a homogenous, acidified sodium chlorite solution. The homogenous, acidified sodium chlorite solution is removed from the mixing chamber and is either utilized as a liquid or is frozen to form ice that is utilized. The acidified sodium chlorite solution provides a slow release of chlorine dioxide gas (ClO 2 ) for use in water treatment, in food plant sanitation, in ice for icing food items, and as an antimicrobial solution for direct application to food items.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims benefit of the filing of U.S. provisionalpatent application Serial No. 60/274,007, filed Mar. 7, 2001, andentitled, “Automatic Metering System For Acidified Sodium Chlorite.”

TECHNICAL FIELD

[0002] This invention relates to a method and apparatus for producingacidified sodium chlorite solutions of predetermined concentrations andtime released properties. The solution provides a slow release ofchlorine dioxide for use in water treatment, in food plant sanitation,in ice for icing food items, and as an antimicrobial solution for directtreatment of food items.

BACKGROUND INFORMATION

[0003] It is known to mix sodium chlorite and mineral acid solutionstogether in a concentrated form. The mixing occurs within a few minutesand the object is to maximize the production of chlorine dioxide fromthe reactants. This concentrate is then diluted with water down toapplication levels of parts per million for use to eliminate spoilageand pathogenic organisms on food items. An object of the presentinvention is to provide a method and apparatus for deliberately mixingthe sodium chlorite and acid solutions in a water stream in such a waythat the chlorine dioxide forms slowly over a period of hours and evendays.

[0004] Known systems for producing and/or using chlorine dioxide aredisclosed in the following United States patents: U.S. Pat. No.4,013,761, granted Mar. 22, 1977 to William J. Ward and Kenneth E.Gasper; U.S. Pat. No. 4,534,952, granted Aug. 13, 1985, to W. HowardRapson and Maurice C. J. Fredette; U.S. Pat. No. 4,925,645, granted May15, 1990, to James A. Mason; U.S. Pat. No. 5,009,875, granted Apr. 23,1991, to Joseph M. Kelley, Donald C. Kucher and George Mayurnik; U.S.Pat. No. 5,618,440, granted Apr. 8, 1997, to James A. Mason; U.S. Pat.No. 5,799,833, granted Sep. 1, 1998, to Thomas S. Green and Eric G.Hilston; U.S. Pat. No. 5,863,584, granted Jan. 26, 1999, to ThomasIverson Jr., Joyce Prindle and Robert E. Keith; U.S. Pat. No. 6,004,604,granted Dec. 21, 1999 to Thomas Iverson Jr., Joyce Prindle and Robert E.Keith; and U.S. Pat. No. 6,120,731, granted Sep. 19, 2000, to Robert D.Kross and Kere Kemp.

DISCLOSURE OF THE INVENTION

[0005] A principal object of the present invention is to produce amethod that is basically characterized by admixing a flowing water andacid solution into a flowing water and sodium chlorite (NaClO₂)solution. The combined solutions are directed into and through a mixingchamber. In the mixing chamber, they are mixed to form a homogeneous,acidified sodium chlorite solution. According to an aspect of theinvention, the homogenous, acidified sodium chlorite solution is removedfrom the mixing chamber and delivered to an environment in whichchlorine dioxide (ClO₂) is desired. In that environment, the chlorinedioxide (ClO₂) is slowly produced by and released from the homogenous,acidified sodium chlorite solution over a period of time.

[0006] According to another aspect of the invention, the flowing waterand acid solution are formed by admixing a flowing acid solution into aflowing water stream. Preferably, about one part acid solution isadmixed with about one thousand eight hundred (1,800) parts of water.Preferably also, about one part sodium chlorite (NaClO₂)solution isadmixed into about one thousand eight hundred (1,800) parts of water.

[0007] The homogenous, acidified sodium chlorite solution may bedelivered from the mixing chamber to an ice maker where it is made intoice. The solution in ice form initially contains less than three parts(and preferably less than one part) per million of free chlorinedioxide. The ice is then delivered to the environment where chlorinedioxide (ClO₂)is desired. In that environment, there is a slow releaseof chlorine dioxide (ClO₂) gas from the ice. The ice is preferably putinto contact with a food item so that the food item will be cooled bythe ice as it melts and will be contacted by the chlorine dioxide(ClO₂)as it is produced.

[0008] The homogenous, acidified sodium chlorite solution may be removedfrom the mixing chamber as a liquid and introduced into water and beused for water treatment. Or, it can be used for food plant sanitation.Also, it can be used as an antimicrobial solution for direct treatmentof food items.

[0009] Another aspect of the invention is to provide an apparatus forproducing a homogeneous, acidified sodium chlorite and water solution.The apparatus is basically characterized by a mixing chamber having aninlet and an outlet, a conduit having an inlet end connected to receivewater under pressure, and an outlet end connected to the inlet of themixing chamber. The apparatus also includes a source of sodium chlorite(NaClO₂), a first feed line leading from said source of sodium chlorite(NaClO₂) to the conduit, and a first feed pump in the first feed line.The apparatus further includes a source of acid solution. A second feedline leads from the source of acid solution to the conduit. It makes aconnection with the conduit between the first feed line to the conduitand the inlet of the mixing chamber. A second feed pump is in the secondfeed line. In use, water under pressure is delivered into the inlet ofthe conduit. The first feed pump is used to pump sodium chlorite(NaClO₂) into the conduit, in admixture with the water in the conduit.The second feed pump is used to feed the acid solution into the conduitin admixture with the sodium chlorite (NaClO₂) and water. The sodiumchlorite (NaClO₂), water and acid solution is then delivered into themixing chamber and in the mixing chamber where it is mixed to homogenizethe solutions.

[0010] In preferred form, at least one flow meter is provided in theconduit upstream of the first feed line. The flow meter produces acontrol signal. The control signal is used to control the first feedpump and may also be used to control the second feed pump. Or, thesystem may include a second flow meter in the conduit upstream of thefirst feed line. In such case, the first flow meter produces a controlsignal that is used to control the first feed pump. The second flowmeter produces a control signal that is used to control the second feedpump.

[0011] According to an aspect of the invention, the conduit is dividedinto two branches which extend for a while as two flow paths. Then, thetwo branches come back together and join a single part of the conduitthat leads into the inlet of the mixing chamber. In such system, thesodium chlorite (NaClO₂) is pumped by the first feed pump into the firstbranch. The acid solution is pumped by the second feed pump into thesecond branch. The second branch delivers the acid solution intoadmixture with the sodium chlorite (NaClO₂) solution that is flowing inthe first branch. The admixture occurs where the first and secondbranches come back together and join the conduit section that leads intothe inlet of the mixing chamber.

[0012] These and other advantages and features will become apparent fromthe detailed description of the best mode for carrying out theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In the drawings, like element designations refer to like partsthroughout the several views, and:

[0014]FIG. 1 is a pictorial view looking into a cabinet that containsthe preferred apparatus for producing an acidified sodium chlorite andwater solution;

[0015]FIG. 2 is a very basic schematic diagram of the system shown byFIG. 1;

[0016]FIG. 3 is a more complete schematic diagram of the system that isshown in FIG. 1;

[0017]FIG. 4 is a view like FIG. 3 but showing a modified system inwhich the conduit that leads from the water intake to the inlet of themixing chamber is divided into two branches, the sodium chlorite (ClO₂)solution is fed into the water in the first branch, the acid solution isdelivered into the water in the second branch, and the branches arecombined into a single conduit section that leads into the inlet of themixing chamber;

[0018]FIG. 5 is a schematic diagram showing the effluent of the mixingchamber being fed into a conduit into admixture with a liquid in theconduit;

[0019]FIG. 6 is a view like FIG. 5 but showing the effluent from themixing chamber being fed into an ice maker and the ice maker deliveringice to a container of a food item that will receive the ice; and

[0020]FIG. 7 is a view like FIGS. 5 and 6 but showing the effluent fromthe mixing chamber being delivered into a container that contains a fooditem or some other item to be treated by the chlorine dioxide (ClO₂)that evolves from the homogeneous, acidified sodium chlorite solution.

DETAILED DESCRIPTION OF THE INVENTION

[0021]FIG. 1 shows a system of the present invention housed within acabinet 10. A conduit 12 delivers a water stream into a conduit C insidethe cabinet 10 that extends from the conduit 12 to the inlet 14 leadinginto a mixing chamber 16. Mixing chamber 16 includes an outlet conduit18 that extends outwardly through an opening in a sidewall of thecabinet 10. Inside the cabinet 10, the conduit C includes a pressureregulator 20 and a standard pressure gauge 22. Flow measuring paddlewheels 24, 26, or any other suitable flow measuring device, are used togenerate and send electrical signals, at a frequency proportional to theflow of water through them, to pulse dividers 28, 30. These adjustablepulse dividers render the number of pulses per minute (or per gallon ofwater) down to a frequency acceptable to chemical feed pumps 32, 34.Feed pump 32 is connected to pump a dilute solution of sodium chlorite(NaClO₂). Pump 34 pumps a mild mineral or organic acid or acidpreparation. The acid solutions are preferably phosphoric acid, citricacid, and any preparations of them containing other ingredients such asdetergents, chelating agents, or other agitives.

[0022] The dilute solution of sodium chlorite (NaClO₂) is delivered by afirst feed line 36 into a region 38 of the conduit C in the cabinet 10.The mild mineral or organic acid or acid preparation is delivered by afeed line 40 into a second region 42 in the conduit that is downstreamof region 38. The reactants are fed separately into the water streamwithin the conduit so as to deliberately avoid mixing the relativelyconcentrated precursor chemicals. Finally, the water stream containingthe reactants are fed into the inlet 14 of the mixing chamber 16 whichacts to smooth out the pulsating delivery by the chemical feed pumps 28,30.

[0023]FIG. 2 shows a source of sodium chlorite (NaClO₂) solution 44 anda source of an acid solution 46. The sodium chlorite (NaClO₂) solution44 is delivered at location 38 in conduit C into admixture with water 48that is delivered to conduit C by conduit 12. There is some mixing ofthe sodium chlorite (NaClO₂) solution 44 with the water 48 before thecombined solutions reach region 42 of conduit C. At region 42, the feedline 40 delivers a water and acid solution 46 into the flowing water andsodium chlorite (NaClO₂) solution that is flowing through the conduit C.The water and acid solution mixes with the water and chlorite (NaClO₂)solution where they flow together in section 50 of conduit C and withinthe mixing chamber 16.

[0024] By way of typical and therefore nonlimitive example, thecomponents shown in FIG. 1 may be as follows. The water pressureregulator 20 may be a ¾″ N35B U, EDP#0006808, 25-75 psi., WattsRegulator Co., North Andover, Mass. 01845. The pressure gauge 22 may bea 2 inch dial, ⅛″ thread, 0-60 psi, BCG Gauges or “over the counter”equivalent. The flow meters 24, 26 may be paddle wheels, SeametricsModel SPX-075225, Seametrics, Inc. 20419 80^(th) Ave. S., Kent, Wash.98032. The pulse dividers 28, 30 may be Seametrics Model PD-10W,Seametrics, Inc. 20419 80^(th) Ave. S., Kent, Wash. 98032. The chemicalfeed pumps 32, 34 may be LMI Milton Roy Model A751-392SI, LMI Milton RoyCo. 8 Post Office Square, Acton, Mass. 01720. The mixing chamber 16 maybe a AMATEK Filter Housing, #10, Clear USFilter, 181 Thornhill Rd.,Warrendale, Pa. 15086.

[0025]FIG. 3 is a more complete schematic diagram of the system shown byFIG. 1. The particular mixing chamber 16 that is illustrated has theinlet 14 and the outlet 18 near its top. However, the inlet 14 feedsdownwardly into a center tube that is open at its lower end. Thesolution flows out of the center tube into an annular chamber thatsurrounds the center tube and flows back upwardly in the annular chamberto the outlet 18. This is but one of a number of types of mixingchambers that can be used.

[0026]FIG. 4 shows a modified system. It is like the system shown byFIG. 3 except that the conduit C divides into two branches C1, C2 andthen combines back into a single conduit section 50 that connects to themixing chamber inlet 14. In this embodiment, feed pipe 36 delivers thesodium chlorite (NaClO₂) solution to water in a branch (or flow path)C1. The feed pipe 40 delivers the acid solution into a conduit branch(or flow path) C2, into admixture with water in that branch C2. Thewater and acid solution is then admixed at 52 into the water and sodiumchlorite (NaClO₂) solution leaving branch C1 and entering into conduitsection 50. In this embodiment, the sodium chlorite (NaClO₂) and theacid are both diluted a considerable amount by water before they arebrought into contact with each other in the conduit section 50.

[0027] In preferred form, a very small amount of NaClO₂ is added to avery large amount of water and a very small amount of the acid solutionis added to a very large amount of water. After being united, the twodilute streams are mixed in the mixing chamber 16 and the combinedsolution is later utilized in one of several manners, as will bedescribed below. This manner of combining the constituents slows theformation of chlorine dioxide (ClO₂). The system of the inventiongenerally does not use strong mineral acids such as hydrochloric acidbecause when such a strong mineral acid is used it will form chlorinedioxide too swiftly for time-release applications. The constituents areslow to act to form the chlorine dioxide gas (ClO₂) and there is a slowrelease of the chlorine dioxide gas (ClO₂). There is a time release.

[0028] Care is taken to produce a strong enough solution to producesufficient chlorine dioxide (ClO₂) to eliminate spoilage and pathogenicorganisms on food items, but at the same time weak enough to prevent anyoxidation of the food items, and weak enough to obtain the desired slow,time release of the chlorine dioxide gas (ClO₂).

[0029] The solutions that are delivered into the mixing chamber 16 aresubstantially thoroughly mixed in the mixing chamber. The effluent ofthe mixing chamber 16 is a substantially homogenous, acidified sodiumchlorite solution. This solution will slowly produce and releasechlorine dioxide gas (ClO₂) over a period of hours and even days. FIG. 5shows the substantially homogenous, acidified sodium chlorite solutionbeing delivered by conduit 60 into admixture with water in a conduit 62.As the sodium chlorite gas (ClO₂) is released in the water, it willpurify the water.

[0030]FIG. 6 shows the effluent from the mixing chamber 16 beingdelivered into an ice maker 74. Ice 66 that is discharged from the icemaker 64 (e.g. as flake ice) contains the acidified sodium chlorite.When the acidified sodium chlorite solution is frozen, the release ofchlorine dioxide gas (ClO₂) is slowed substantially and will usuallyoccur over a period of days. When the acidified sodium chlorite solutionis not frozen, the chlorine dioxide gas (ClO₂) will be released over aperiod of hours, or at least fastener than it is released from ice. FIG.6 shows the ice 62 being delivered into a vessel 68 that may contain afood item, such as meat, fish, or a vegetable. The ice keeps the fooditem cold and when the chlorine dioxide gas (ClO₂) is released, itcontacts and treats the food item.

[0031]FIG. 7 shows the effluent 60 from the mixing chamber beingintroduced into or onto a space 70, into contact with a food item, toserve as an antimicrobial solution for direct treatment of the fooditem. The region 70 may be a container or a region on a conveyor usedfor conveying the food item. In this installation, the effluent can besprayed onto the food item, such as disclosed in the aforementioned U.S.Pat. No. 5,863,584, for example.

[0032] While specific embodiments of the present invention have beenshown and described in detail to illustrate the utilization of theinventive principles, it is to be understood that such showing anddescription have been offered by way of example, and not by way ofstrict limitation. Protection by Letters Patent of this invention andall of its aspects are set forth in the appended claims and is sought tothe broadest extent that the prior art allows.

What is claimed is:
 1. A method of producing an acidified sodiumchlorite and water solution, comprising: admixing a flowing water andacid solution into a flowing water and sodium chlorite (NaClO) solution;flowing the combined solutions into and through a mixing chamber to forma homogenous, acidified sodium chlorite solution in the mixing chamber;and removing the homogenous, acidified sodium chlorite solution from themixing chamber.
 2. The method of claim 1, comprising forming the flowingwater and acid solution by admixing a flowing acid solution into aflowing water stream.
 3. The method of claim 2, comprising admixingabout one part acid solution to about one thousand eight hundred (1,800)parts of water.
 4. The method of claim 3, comprising admixing about onepart sodium chlorite (NaClO₂) solution to about one thousand eighthundred (1,800) parts of water.
 5. The method of claim 1, comprisingadmixing about one part sodium chlorite (NaClO₂) solution to about onethousand eight hundred (1,800) parts of water.
 6. The method of claim 5,comprising forming the flowing water and acid solution by admixing aflowing acid solution into a flowing water stream.
 7. A method ofproducing chlorine dioxide slowly over a period of time, comprising:admixing a flowing water and acid solution into a flowing water andsodium chlorite (NaClO₂) solution; flowing the combined solutions intoand through a mixing chamber to form a homogenous, acidified sodiumchlorite solution in the mixing chamber; and removing the homogenous,acidified sodium chlorite solution from the mixing chamber anddelivering it to an environment in which chlorine dioxide (ClO₂) isdesired, whereby in such environment the chlorine dioxide (ClO₂) will beslowly produced by and released from the homogenous, acidified sodiumchlorite solution, over a period of time.
 8. The method of claim 7,comprising delivering the homogenous, acidified sodium chlorite solutionto an ice maker, freezing it in the ice maker to make ice in which thefree chlorine dioxide content is initially less than three parts permillion, and then delivering the ice to the environment where chlorinedioxide (ClO₂) is desired, whereby there is a slow release of chlorinedioxide (ClO₂) gas from the ice as the ice melts.
 9. The method of claim8, comprising putting the ice into contact with a food item, so that thefood item will be cooled by the ice and will be contacted by thechlorine dioxide (ClO₂) as it is produced.
 10. The method of claim 7,comprising forming the flowing water and acid solution by admixing aflowing acid solution into a flowing water stream.
 11. The method ofclaim 10, comprising admixing about one part acid solution to about onethousand eight hundred (1,800) parts of water.
 12. The method of claim11, comprising admixing about one part sodium chlorite (NaClO₂) solutionto about one thousand eight hundred (1,800) parts of water.
 13. Themethod of claim 7, comprising admixing about one part sodium chlorite(NaClO₂) solution to about one thousand eight hundred (1,800) parts ofwater.
 14. The method of claim 13, comprising forming the flowing waterand acid solution by admixing a flowing acid solution into a flowingwater stream.
 15. The method of claim 8, comprising forming the flowingwater and acid solution by admixing a flowing acid solution into aflowing water stream.
 16. The method of claim 15, comprising admixingabout one part acid solution to about one thousand eight hundred (1,800)parts of water.
 17. The method of claim 16, comprising admixing aboutone part sodium chlorite (NaClO₂) solution to about one thousand eighthundred (1,800) parts of water.
 18. The method of claim 8, comprisingadmixing about one part sodium chlorite (NaClO₂) solution to about onethousand eight hundred (1,800) parts of water.
 19. The method of claim18, comprising forming the flowing water and acid solution by admixing aflowing acid solution into a flowing water stream.
 20. The method ofclaim 15, comprising putting the ice into contact with the food product,so that the food product will be cooled by the ice and will be contactedby the chlorine dioxide (ClO₂) as it is produced.
 21. The method ofclaim 16, comprising putting the ice into contact with a food product,so that the food product will be cooled by the ice and will be contactedby the chlorine dioxide (ClO₂) as it is produced.
 22. The method ofclaim 17, comprising putting the ice into contact with a food product,so that the food product will be cooled by the ice and will be contactedby the chlorine dioxide (ClO₂) as it is produced.
 23. The method ofclaim 18, comprising putting the ice into contact with a food product,so that the food product will be cooled by the ice and will be contactedby the chlorine dioxide (ClO₂) as it is produced.
 24. The method ofclaim 19, comprising putting the ice into contact with a food product,so that the food product will be cooled by the ice and will be contactedby the chlorine dioxide (ClO₂) as it is produced.
 25. The method ofclaim 7, wherein the environment is a food plant environment, whereby insuch environment the chlorine dioxide (ClO₂) will be slowly produced andreleased from the homogenous, acidified sodium chlorite solution over aperiod of time and will sanitize the food plant.
 26. The method of claim7, wherein the environment includes food items that are positioned to becontacted by the chlorine dioxide (ClO₂) as it is produced, whereby thechlorine dioxide (ClO₂) will act as an antimicrobial solution for directtreatment of the food item.
 27. Apparatus for producing a homogenous,acidified sodium chlorite and water solution, comprising: a mixingchamber having an inlet and an outlet; a conduit having an inlet endconnected to receive water under pressure, and an outlet end connectedto the inlet of the mixing chamber; a source of sodium chlorite(NaClO₂); a first feed line leading from said source of sodium chlorite(NaClO₂) to the conduit; a first feed pump in the first feed line; asource of acid solution; a second feed line leading from the source ofacid solution to the conduit, between the connection of the first feedline to the conduit and the inlet of the mixing chamber; and a secondfeed pump in the second feed line, whereby the water under pressure canbe delivered into the inlet of the conduit, the first feed pump can beused to pump sodium chlorite (NaClO₂) into the conduit, in admixturewith the water in the conduit, whereby said second feed pump can feedthe acid solution into the conduit in admixture with the sodium chlorite(NaClO₂) and water, whereby the sodium chlorite (NaClO₂), water and acidsolution can be delivered into the mixing chamber, and whereby saidmixing chamber can be used to homogenize the solutions to produce anhomogenous, acidified sodium chlorite and water solution, for deliveryout through the outlet of the mixing chamber.
 28. The apparatus of claim27, comprising a flow meter in the conduit upstream of the first feedline, said flow meter producing a control signal that is used to controlthe first feed pump, and a flow meter in the conduit upstream of thefirst feed line, said flow meter produces a control signal that is usedto control the second feed pump.
 29. The apparatus of claim 28,comprising two flow meters, one for each feed pump.
 30. The apparatus ofclaim 27, wherein the conduit separates into parallel flow branches andthe branches later recombine at a location in the conduit upstream ofthe inlet of the mixing chamber, wherein the first feed line feedssodium chlorite (NaClO₂) into a first of said branches and the secondfeed line feeds acid solution into the second of said branches, wherebythe second feed line and the portion of the second branch downstream ofthe second feed line deliver an acid and water solution into the conduitwhere the first and second conduits come back together and wherein theacid and water solution are admixed to a sodium chlorite (NaClO₂) andwater solution that is flowing through the first branch back into theconduit downstream of the branches.